Thermometers which utilize thermistors for temperature determinations have been developed for the principal purpose of measuring temperatures in medical applications. Therefore, in such cases an effort must be made to keep production of the thermistors, and the thermometers produced therefrom, simple and cheap enough so that the thermometers can be thrown away after use. That is, it must be possible to discard the thermometers and not reuse them.
At the same time, it still remains necessary to be able to produce these thermistors and thermometers with the required degree of accuracy and so that the temperature value read therefrom can be relied upon, as is of course of great significance in the medical field. Those having knowledge of this business will understand that thermometers made in accordance with this invention can also be used in other connections, such as for purely industrial applications where a simple and cheap thermometer can be prepared but which remains capable of producing a reliable temperature reading.
In U.S. Pat. Nos. 4,317,367; 4,296,633 and 4,253,334; and in U.S. patent application Ser. No. 196,079, which was filed on Sept. 25, 1980, now U.S. Pat. No. 4,382,246 several designs for thermometers are described in which a thermistor is used, and in which thermistors made in accordance with the present invention could be utilized. Furthermore, U.S. Pat. Nos. 4,200,970 and 4,236,298 disclose processes for adjusting thermistors which are to be fitted as temperature sensors in other thermometer designs therefor. However, these and other known processes for adjusting thermistors and the like suffer from the disadvantage that heat is developed in any mechanical processing utilized in order to adjust the electrical property, such as resistance, of the temperature sensitive portions of these sensors. Thus, it becomes quite difficult to measure these properties as a control at a precisely predetermined temperature.
Furthermore, British Pat. No. 796,357 discloses another process for manufacturing resistors from a composite web which is produced from superimposed ribbons of resinous material having conductive material dispersed therein, as shown in FIG. 1 thereof. These ribbons are then cut into strips m by guillotine 1, and their resistances are then measured. A feedback control unit p is then used to vary the size of the sliced strips in response thereto.
It is an object of the present invention to remove or at least reduce the dependence on the relatively complicated adjustment processes of the prior art. This is now done by providing additional accuracy in the manufacturing process, which can also now be carried out in combination with a simple sorting process for combining two or more sensors in accordance with a method which is similar to that of U.S. Pat. No. 4,302,972.